<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .inner{
            border: 1px solid #000;
            line-height: 30px;
            height: 30px;
            width: 200px;
        }
        .inner:first-child{
            color: red;
        }
        .inner:last-child{
            color: green;
        }
        /* 它的下标不是从0开始,而是从1开始 */
        .inner:nth-child(2){
            color: aquamarine;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="inner">我是子盒子1</div>
        <div class="inner">我是子盒子2</div>
        <div class="inner">我是子盒子3</div>
        <div class="inner">我是子盒子4</div>
        <div class="inner">我是子盒子5</div>
    </div>
</body>
</html>